Phorbol esters which activate protein kinase C (PKC) have been shown to enhance experimental lung metastasis. Therefore, it was logical that inhibitors of PKC might also modulate metastasis. The later possibility was investigated with the pyridyloxazole-2-one, 4-propyl-5(4-pyridinyl)-2(3H)-oxazolone, as well as with the PKC inhibitors H-7 and staurosporine.